Custom Quest is a plugin for Unity. It aims to fulfill any needs a developer could have for a quest system.
Find Custom Quest here
Documentation (API) can be found here here.*
guides and explanations of use can be found menu on the left.
One of the major features of the system, is the ability to easily expand and customize each individual quest as needed. You can even add new code, without touching the core!
Custom Quest is no longer being supported by Random Dragon, it is however free to use and download on the asset store.